The present disclosure relates to an attachment unit.
A known connection device connects a post-processing device to a main body of an image forming apparatus. The connection device includes a fixed locking member and a movable locking member. The fixed locking member is connected to a first frame of the post-processing device. The movable locking member is in contact with an outer face of the fixed locking member and is slidable. A positioning pin fixed to a second frame of a copier, which is an example of the image forming apparatus, is inserted in a pin insertion hole and a large diameter portion in the movable locking member in an unlock position. The positioning pin engages with and is fixed to a small diameter portion in the movable locking member when the movable locking member is moved to slide to a lock position with the positioning pin in the pin insertion hole.